This invention relates to a device for measuring thermal conductivity of liquids, and more particularly to a thermal conductivity measuring device of the laser flash heating type in which a sample liquid is heated by impulsive light from a laser (laser flash).
In the conventional laser flash heating type measuring device of this class, a sample liquid, for instance, mercury is sealed in a container of boron nitride with a lid of a transparent quartz plate and irradiated from above by a laser flash, while measuring the response in temperature rise at the bottom surface of the sample mercury layer by a thermocouple which has its detecting end at the bottom of the container.
However, such conventional measuring device has the following problems.
(1) The measurement is possible only with an opaque liquid like mercury which is impermeable to laser light and which can receive the energy of the irradiated laser flash at its surface, and not with most of other liquids which are permeable to the laser light.
(2) Where a liquid of good thermal conductivity like a liquid metal is to be measured, it is easy to choose a container material with a thermal conductivity low enough as compared with that of the sample liquid. However, many of other liquids do not have much difference in thermal conductivity from the container which holds the sample, making it difficult to obtain the heat conductivity and thermal diffusivity of a sample from the measurement of temperature response.
(3) It is extremely difficult to seal up the sample liquid in the container and a thin gas absorption layer is apt to be formed between the sample liquid and the wall surfaces of the container, producing a contact resistance which causes unignorable errors to the measured values.
(4) Strict assessment of the thickness of the sample liquid layer is required in analyzing the measured temperature response, so that it is necessary to know precisely the thermal expansion coefficient of the container. In addition, there is a possibility of the sample liquid overflowing from the container or of a void space being formed within the container when the measuring temperature is changed, due to the difference in thermal expansion coefficient between the container material and the sample liquid.